Spacer for rolling bearing, notably used in a wind turbine

ABSTRACT

The spacer is adapted for a rolling bearing comprising an inner ring, an outer ring and at least one row of angular contact rollers disposed between raceways and guiding faces provided on the rings. The spacer comprises opposite inner and outer parts  13, 14  and opposite lateral flanges  15, 16  respectively adapted to come into contact with the raceways and the guiding faces of the rings. Said inner and outer parts and/or said lateral flanges comprise at least a contact surface  14   a,    14   b;    16   a  with one of the rings and a concave recess  14   c;    16   b,    16   c,    16   d  directed outwards towards said ring.

The present invention relates to the field of rolling bearings, inparticular rolling bearings having an inner ring and an outer ring withone or more rows of contact rollers therebetween.

The invention relates more particularly to the field of large-diameterrolling bearings adapted to be used in a wind turbine.

In such application, rolling bearings are used to angularly orient therotor of the turbine according to the direction of the wind, and toorient the blades of the turbine around their longitudinal axes. Suchrolling bearings are loaded mainly by a stress, both axially andradially, often with a relatively strong load.

A rolling bearing for a wind turbine comprise two concentric inner andouter rings, at least a row of oblique contact rollers arranged betweenraceways and guiding faces provided on said rings, and a plurality ofspacers disposed circumferentially between the rollers. Each spacergenerally comprises two opposite cavities having a concave profileadapted to the rollers and delimited axially by lateral flanges, and twoopposite inner and outer planar surfaces.

Said planar surfaces and lateral flanges of each spacer may respectivelycome into contact with the raceways and the guiding faces of the rings.Such contacts between the spacers and the rings induce an increase ofthe friction torque of the rolling bearing.

It is a particular object of the present invention to provide a spacerfor rolling bearing adapted to reduce its friction contribution andwhich is simple to manufacture and economic.

In one embodiment, the spacer for rolling bearing comprising an innerring, an outer ring and at least one row of angular contact rollersdisposed between raceways and guiding faces provided on the rings,comprises opposite inner and outer parts and opposite lateral flangesrespectively adapted to come into contact with the raceways and theguiding faces of the rings. Said inner and outer parts and/or saidlateral flanges comprise at least a contact surface with one of therings and at least a concave recess directed outwards towards said ring.

The spacer may comprise two opposite faces having a concave profileadapted to the rollers. Advantageously, the recess extends from one faceto the other. Preferably, the opposite faces are delimited axially bythe lateral flanges and connected to the inner and outer parts.

In one embodiment, each face comprises a recess extending from the innerpart to the outer part. The spacer may comprise a through-hole puttingthe faces into communication.

In one preferred embodiment, the inner and outer parts and/or thelateral flanges each comprise at least a contact surface with one of therings and at least a recess directed towards said ring.

In one embodiment, the inner and outer parts each comprise two contactsurfaces and a recess disposed therebetween. Alternatively or incombination, the lateral flanges may each comprise one contact surfaceand a recess in a form of a groove formed onto said surface.Advantageously, the lateral flanges each further comprise additionalrecesses located on the both sides of the contact surface.

In one embodiment, the spacer is formed in one part from metal or frompolymer material.

In another aspect of the invention, a rolling bearing comprises an innerring, an outer ring, at least one row of angular contact rollersdisposed between raceways and guiding faces provided on the rings, and aplurality of spacers as previously defined and disposedcircumferentially between the rollers.

In one preferred embodiment, the recesses of the spacers are filled withlubricant.

The rolling bearing as previously defined may be particularly useful asa bearing for a wind turbine comprising a mast holding a nacelle whereblades are installed, in particular for rotating the nacelle withrespect to the mast and/or for rotating/pitching each blade around itslongitudinal axis.

The present invention and its advantages will be better understood bystudying the detailed description of a specific embodiment given by wayof non-limiting example and illustrated by the appended drawings onwhich:

FIG. 1 is a half section of a rolling bearing according to an example ofthe invention,

FIG. 2 is a half section of the rolling bearing of FIG. 1 according toanother section plan,

FIG. 3 is a part section on a larger scale of FIG. 2,

FIG. 4 is a perspective view of a spacer of the rolling bearing of FIGS.1 and 2,

FIG. 5 is a perspective view of the spacer of FIG. 4 with two associatedrollers,

FIG. 6 is a side view of FIG. 5, and

FIG. 7 is a view in section on VII-VII of FIG. 6.

The rolling bearing as illustrated on the FIGS. 1 and 2 is alarge-diameter rolling bearing comprising an inner ring 1 and an outerring 2 between which are housed two rows of oblique or angular contactrollers 3 a and 3 b. The rolling bearing also comprises a plurality ofspacers 4 disposed circumferentially between the rollers 3 a, 3 b tomaintain the circumferential spacing between them.

The inner and outer rings 1, 2 are concentric and extend axially alongthe bearing rotation axis (not shown) of the rolling bearing. The rings1, 2 are of the solid type. A “solid ring” is to be understood as a ringobtained by machining with removal of material (by machining, grinding)from metal tube stock, bar stock, rough forgings and/or rolled blanks.

The rollers 3 a, 3 b are identical with one another and each comprise anexterior rolling surface and opposite end transverse faces delimitingaxially the rolling surface. In the illustrated embodiment, the rollingsurfaces have a cylindrical profile. Alternatively, the rolling surfacesmay have a spherical profile or a logarithmic profile. For each row, therotation axes 3′a, 3′b of the rollers converge in one single pointlocated on the longitudinal axis of the bearing, and are disposed at adetermined angle with respect to the bearing axis. In the illustratedembodiment, the rotation axes 3′a, 3′b of the rollers of the two rowsare arranged at an angle of 90° to each other, and of approximately of45° to the bearing axis. The angle between the rotation axis 3′a, 3′b ofeach roller and the bearing axis may be comprised for example between20° and 70°.

The inner ring 1 has a bore 1 a of cylindrical shape designed to befixed to a chassis or to a structure of a machine (not shown) anddelimited by opposite radial lateral surfaces 1 b, 1 c. The inner ring 1also comprises a stepped exterior cylindrical surface 1 d onto whichfirst and second annular raceways 5, 6 are formed. The raceways 5, 6 aremutually symmetric with respect to a transverse radial plane passingthrough the centre of the rolling bearing. Each raceway 5, 6 extendobliquely inwards from the exterior cylindrical surface 1 d and has afrustoconical shape. Each raceway 5, 6 has in cross section a straightinternal profile in contact with the rolling surfaces of the rollers 3a, 3 b.

The outer ring 2 comprises an outer cylindrical surface 2 a delimited byopposite radial lateral surfaces 2 b, 2 c. The outer ring 2 alsocomprises a stepped annular bore 2 d of cylindrical shape into whichfirst and second raceways 7, 8 are formed. The raceways 7, 8 aremutually symmetric with respect to the radial plane passing through thecentre of the rolling bearing. The raceways 7, 8 are respectivelyparallel to the raceways 5, 6. Each raceway 7, 8 extends obliquelyoutwards from the bore 2 d and has a frustoconical shape. Each raceway7, 8 has in cross section a straight internal profile in contact withthe rolling surfaces of the rollers 3 a, 3 b. The raceways 5, 6 of theinner ring and the raceways 7, 8 of the outer ring mutually face eachother while at the same time being symmetric with regard to the rotationaxis 3′a, 3′b of the rollers 3 a, 3 b.

The inner ring 1 also comprises annular guiding faces 9, 10 formed ontothe exterior surface 1 d and which may be in axial contact with the endfaces of the rollers with regard to the rotation axes 3′a, 3′b. Theguiding faces 9, 10 are mutually symmetric with respect to the radialplane passing through the centre of rolling bearing. Each guiding face9, 10 is straight and disposed perpendicular to the correspondingraceway 5, 6 and is connected to the edge of small diameter of saidraceway by an annular concave fillet. Each guiding face 9, 10 extendsobliquely outwards from said fillet and is connected to the exteriorsurface 1 d of the inner ring. The guiding faces 9, 10 extend radiallyrelative to the rotation axis 3′a, 3′b of the rollers. Each guidingfaces 9, 10 and the associated raceway 5, 6 delimit a V-shaped groovedirected radially outwards.

The outer ring 2 also comprises guiding faces 11, 12 formed into thebore 2 d and which may be in axial contact with the opposite end facesof the rollers 3 a, 3 b with regard to the rotation axes 3′a, 3′b. Theguiding faces 11, 12 are mutually symmetric with respect to the radialplane passing through the centre of rolling bearing. The guiding faces11, 12 and the guiding faces 9, 10 mutually face each other and arerespectively parallel. Each guiding face 11, 12 is straight and disposedperpendicular to the corresponding raceway 7, 8 and is connected to theedge of large diameter of said raceway by an annular concave fillet.Each guiding face 11, 12 extends obliquely inwards from said fillet andis connected to the bore 2 d of the inner ring. Each guiding face 11, 12extend radially relative to the rotation axis 3′a, 3′b of the rollers.Each guiding face 11, 12 and the associated raceway 7, 8 delimit aV-shaped groove directed radially inwards.

The raceway 5 and the guiding face 9 of the inner ring define togetherwith the raceway 7 and the guiding face 11 of the outer ring a firstannular space inside which the row of rollers 3 a is disposed. Eachroller 3 a arranged between the raceways 5, 7 is maintained laterally inposition by the guiding faces 9, 11 to avoid a skewing or tilting ofsaid roller with respect to the raceways. Each guiding face 9, 11 form aflank having a direct contact surface with the associated end face ofthe rollers 3 a to have a slight relative sliding between the end facesof rollers and the inner and outer rings 1, 2.

Similarly, the raceway 6 and the guiding face 10 of the inner ringdefine together with the raceway 8 and the guiding face 12 of the outerring a second annular space inside which the row of rollers 3 b isdisposed. The arrangement of the rollers 3 b with respect to the guidingfaces 10, 12 is the same that the one previously described for therollers 3 a and the guiding faces 9, 11.

The spacers 4 are identical with one another and each placed between twoconsecutive rollers 3 a, 3 b of each row. The spacers 4 may be made inone part from metal. Alternatively, the spacers 4 may be made frompolymer material such as polyamide, for instance by moulding.

As shown on FIGS. 2 to 4, each spacer 4 comprises two opposite inner andouter parts 13, 14 coming into contact with the facing raceways of theinner and outer rings 1 and 2, and two opposite lateral flanges 15, 16coming into contact with the opposite guiding faces of said rings. Eachspacer 4 also comprises two opposite faces 17, 18 adapted to receive twoconsecutive rollers. With regard to the rotation axes of said rollers,the faces 17, 18 are delimited axially by the lateral flanges 15, 16.The faces 17, 18 are delimited transversally by the inner and outerparts 13, 14.

As shown on FIG. 3, for the row of rollers 3 a, the inner and outerparts 13, 14 of each spacer come into contact with the inner and outerraceways 5, 7 and the lateral flanges 15, 16 come into contact with theguiding faces 9, 11. The raceways 5, 7 and the guiding faces 9, 11 eachform a flank having a direct contact surface with the associated part13, 14 or flange 15, 16 to have a slight relative sliding between eachspacer 4 and the rings 1, 2. In order to limit the induced frictiontorque of the spacers 4, a slight clearance is foreseen between eachspacer and the raceways 5, 7 and the guiding faces 10, 12 of the rings.The arrangement of the spacers 4 for the row of rollers 3 b with respectto the raceways 6, 8 and to the guiding faces 10, 12 of the rings is thesame that the one described for row of rollers 3 a.

As shown on FIGS. 3 and 4, the outer part 14 of each spacer comprisestwo identical and separate planar contact surfaces 14 a, 14 b bearingagainst the associated raceway of the outer ring 2 and a concave recess14 c extending therebetween and which faces said raceway while remainingdistant from the latter. In the illustrated embodiment, the recess 14 chas in cross-section a U-shape. The recess 14 c extends transversallyfrom a longitudinal edge of the contact surface 14 a to a facinglongitudinal edge of the other contact surface 14 b, and longitudinallyfrom the face 17 to the other face 18.

With the concave recess 14 c, the friction contacts between the outerpart 14 of each spacer and the associated raceway of the outer ring 2are reduced. Besides, the recess 14 c advantageously acts as lubricantreservoir for lubricating the contact surfaces 14 a, 14 b of the outerpart, the associated raceway of the outer ring 2 and the rollingsurfaces of the rollers 3 a and 3 b, the lubricant emerging from therecess directly onto said contact and rolling surfaces and said raceway.The lubricant used (not shown) may be for example grease or oil.

Since the inner and outer parts 13, 14 of each spacer are identical inthe illustrated embodiment, only one of them is described here, it beingunderstood that the references “a, b, c” previously used for the outerpart 14 are also used for the identical elements of the inner part 13.For the same reasons, only one of lateral flanges 15, 16 will bedescribed, it being understood that the same references “a, b, c, d” areused for the identical elements of the two flanges.

The lateral flange 15 comprises a central planar contact surface 15 abearing against the associated guiding face of the inner ring, twoidentical concave recesses 15 b, 15 c which face said ring whileremaining distant from the latter, and a groove 15 d provided on thecontact surface 15 a. The distance separating the contact surfaces 15 aand 16 a of the two flanges 15, 16 is substantially equal to the lengthof the rollers 3 a, 3 b.

The recess 15 b extends from a first edge of the contact surface 15 a toa longitudinal edge of the contact surface 14 b of the outer part 14which is opposite to the longitudinal edge of said surface connected tothe recess 14 c. The recess 15 c extends from a second opposite edge ofthe contact surface 15 a to a longitudinal edge of the contact surface13 b which is opposite to the longitudinal edge of said surfaceconnected to the recess 13 c. The recesses 15 b, 15 c extendlongitudinally from the face 17 to the other face 18. The distanceseparating the two edges of the contact surface 15 a is substantiallyequal to the length of the associated guiding face of the inner ring.The groove 15 d is directed outwards and faces said guiding face whileremaining distant from the latter. The groove 15 d extendslongitudinally from the face 17 to the other face 18 and has incross-section a concave internal profile in the shape of a semi-circle.

As shown on FIG. 3, for the row of rollers 3 a, the contact surface 15 aof the lateral flange 15 comes into contact with the guiding face 9 ofthe inner ring 1, and the recess 15 c faces the concave fillet whichconnects said guiding face and the raceway 5 while remaining distantfrom said fillet. The recess 15 b is oriented towards the exteriorsurface 1 d of the inner ring.

With the concave recess 15 c and the concave groove 15 d, the frictioncontacts between the lateral flange 15 and the inner ring 1 are reduced.Besides, the recesses 15 b, 15 c and the groove 15 d advantageously actas lubricant reservoirs for lubricating the contact surface 15 a, theguiding face 9 of the inner ring and the end faces of the rollers. Thelubricant (not shown) emerges from the recesses 15 b, 15 c and thegroove 15 d directly onto the contact surface 15 a, the guiding face 9and the end faces of the rollers.

For the row of rollers 3 a, the contact surface 16 a of the lateralflange 16 bears against the guiding face 11 of the outer ring 2, and therecess 16 b faces the concave fillet which connects said guiding faceand the raceway 7 while remaining distant from said fillet. The recess16 c is oriented towards the bore 2 d of the outer ring. The recesses 16b, 16 c and the groove 16 d also act as reservoirs filled with lubricant(not shown).

Since the faces 17, 18 of each spacer are identical in the illustratedembodiment, only one of them is described here, it being understood thatthe same references “a, b, c” are used for the identical elements of thetwo faces.

As shown on FIGS. 4 and 5, the face 17 comprises two identical andseparate concave contact surfaces 17 a, 17 b having the shape of coaxialcylinder segments and a profile corresponding to the profile of therolling surface of the associated roller 3 a. The axis of the cylindersegments of the contact surfaces 17 a, 17 b is parallel to the axis ofthe cylinder segments of the contact surfaces 18 a, 18 b. Eachcircumferential end of each concave contact surfaces 17 a, 17 b isextended by a plane surface (not referenced) connected to a transversaledge of the associated planar contact surface 13 a, 14 a, 13 b, 14 b.The face 17 also comprises a concave recess 17 c extending between saidcontact surfaces and which faces the roller 3 a while remaining distantfrom the rolling surface of the latter. In the illustrated embodiment,the recess 17 c has in cross-section a U-shape. The recess 17 c extendstransversally from a longitudinal edge of the contact surface 17 a to afacing longitudinal edge of the other contact surface 17 b. The recess17 c extends from the recess 13 c of the inner part 13 to the recess 14c of the outer part 14. A joint edge of the recess 17 c and the recess14 c is offset inwards with regard to the contact surfaces 14 a, 14 b ofthe outer part 14 and to the circumferential ends of the contactsurfaces 17 a, 17 b of the face 17. Similarly, a facing joint edge ofthe recess 17 c and the recess 13 c is offset inwards with regard to thecontact surfaces 13 a, 13 b of the inner part 13 and to thecircumferential ends of the contact surfaces 17 a, 17 b of the face 17.

With the concave recess 17 c, the friction contacts between the face 17of each spacer and the associated roller are reduced. Besides, therecess 17 c advantageously acts as lubricant reservoir for lubricatingthe concave contact surfaces 17 a, 17 b of the face and the rollingsurface of the roller, the lubricant (not shown) emerging from therecess 17 c directly onto said contact and rolling surfaces. Besides,the lubricant emerging from the recess 17 c may be moved outward bycentrifugal effect and reach the planar contact surfaces 14 a, 14 b ofthe outer part 14 and the associated raceway of the outer ring 2.

Each spacer 4 further comprises a through-hole 19 made inside itsthickness, which opens onto the faces 17, 18 and put said faces intocommunication. On each face the through-hole 19 opens onto the recess 17c, 18 c and the facing longitudinal edges of the contact surfaces 17 a,17 b and 18 a, 18 b. Some lubricant (not shown) is disposed inside thethrough-hole 19, said hole acting as lubricant reservoir for lubricatingthe rolling surfaces of the two rollers associated to each spacer andthe associated concave contact surfaces. The through-hole 19 allows thelubricant contained to emerge directly onto the rolling surface of eachroller and the concave contact surfaces.

Otherwise, the recesses 15 b to 15 d of the lateral flange 15 of thespacer open onto the opposite concave contact surfaces 17 b, 18 b of thefaces. Similarly, the recess 16 b to 16 d of the lateral flange 16 openonto the opposite concave contact surfaces 17 a, 18 a of said faces.Hence, the lubricant contained into the above-mentioned recesses mayalso emerge directly onto the concave contact surfaces of the faces 17,18 and the end faces and the rolling surfaces of the associated rollers.

For each spacer 4, the presence of the recesses on the inner and outerparts 13, 14 and on the lateral flanges 15, 16 makes it possible toreduce the friction contacts with the rings, and to have a significantreserve of lubricant closed to the rollers 3 a, 3 b and to the racewaysand the guiding faces of the rings. The friction contribution of eachspacer 4 with regard to the inner and outer rings is thus reduced.

Otherwise, the presence of the recesses 17 c, 18 c on each spacer makesit possible to reduce the friction contacts with the rollers and to havea significant reserve of lubricant closed to the concave contactsurfaces 17 a, 17 b and 18 a, 18 b and the rolling surfaces of saidrollers. The friction contribution of each spacer 4 with regard to therollers is thus reduced. Alternatively, it may however be possible tonot foresee the recesses 17 c, 18 c on the spacers.

The general structure of each spacer 4 is lightened by the recesses. Aweight reduction for each spacer is obtained. In the illustratedembodiment, each spacer 4 has a first symmetry plane passing through thegrooves 15 d, 16 d of the lateral flanges and parallel to the planarcontact surfaces of the inner and outer parts 13 and 14, a secondsymmetry plane passing through the recesses 13 c, 14 c and perpendicularto the first plane, and a third symmetry plane passing through therecesses 17 c, 18 c and parallel to the planar contact surfaces of thelateral flanges 15 and 16.

For the introduction of the rollers 3 a, 3 b and the associated spacers4 into the first and the second annular spaces defined between the innerand outer rings 1 and 2, said outer ring comprises two filling orifices(not shown) each extending radially from the outer cylindrical surface 2a and opening into one of the annular spaces delimited by the racewaysand the guiding faces. The outer ring also comprises two plugs closingthe filling orifices and each comprising two planar surfaces whichrespectively replace locally the raceway and the guiding face of theouter ring.

As shown on FIGS. 1 and 2, the inner and outer rings 1, 2 furtherrespectively comprise axial holes 20, 21 for fixing the two rings to twoparts of a machine which can rotate one with respect to the other byvirtue of the rolling bearing.

The rolling bearing further comprises two annular seals 22, 23positioned radially between the inner and outer rings 1, 2. The seal 22is mounted axially between the rollers 3 a and the radial surface 2 b ofthe outer ring 2. The seal 23 is positioned axially between the rollers3 b and the radial surface 1 c of the inner ring 1. In the disclosedembodiment, the seal 23 is identical to the seal 22 and is positionedsymmetrically with respect to the latter with regard to the radial planepassing through the center of the rolling bearing. Alternatively, theseal 23 may be different from the seal 22 with a different shape. Aclosed space is defined between the rings 1, 2 and the seals 22, 23 inwhich the rollers 3 a, 3 b are housed so as to be protected againstpolluting elements. In the disclosed embodiment, the seals 22 and 23have in cross-section the overall shape of a H.

Although the invention has been illustrated on the basis of a rollingbearing having a double row of oblique contact rollers, it should beunderstood that the invention can be applied to bearings having a simplerow of rollers or at least three rows of rollers. Otherwise, in theillustrated embodiments, the rolling bearings are O-type bearings.Alternatively, it may also be possible to foresee X-type rollingbearings.

Furthermore, the inner ring and/or the outer ring may comprise gearingteeth on their outer periphery, so as to be connected to driving gearsfor instance connected to the output shaft of a motor. In anotherembodiment, the inner ring and/or the outer ring may be connected to ajack, for example a hydraulic or pneumatic jack.

Thanks to the invention, the friction of the rolling bearing is reduced.This is particularly advantageous in the case of a wind turbinecomprising actuation means for changing the pitch of the blades, becauseit allows to downsize these actuation means since less power is requiredto pitch the blades, and even to reduce the response time of thispitching action, with, as a consequence, an improved overall efficiencyof the wind turbine.

1. A spacer for a rolling bearing comprising: an inner ring, an outerring, at least one row of angular contact rollers disposed betweenraceways and guiding faces provided on the rings, and opposite inner andouter parts and opposite lateral flanges respectively adapted to comeinto contact with the raceways and the guiding faces of the rings, theinner and outer parts and/or the lateral flanges providing at least acontact surface with one of the rings and at least a concave recessdirected outwards towards the ring.
 2. The spacer according to claim 1,further comprising two opposite faces having a concave profile adaptedto the rollers.
 3. The spacer according to claim 2, wherein the recess(14 c; 16 b, 16 c, 16 d) extends from one face to the other.
 4. Thespacer according to claim 3, wherein the opposite faces are delimitedaxially by the lateral flanges and connected to the inner and outerparts.
 5. The spacer according to claim 4, wherein each face furthercomprises a recess extending from the inner part to the outer part. 6.The spacer according to claim 5, further comprising a through-holealigning the faces into communication.
 7. The spacer according to claim6, wherein the inner and outer parts and/or the lateral flanges eachincludes at least a contact surface with one of the rings and at least arecess directed towards the ring.
 8. The spacer according to claim 7,wherein the inner and outer parts each include two contact surfaces anda recess disposed therebetween.
 9. The spacer according to claim 8,wherein the lateral flanges each include one contact surface and arecess in a form of a groove formed onto said surface.
 10. The spaceraccording to claim 9, wherein the lateral flanges each further compriseadditional recesses located on the both sides of the contact surface.11. The spacer according to claim 10, further comprising being formedfrom metal or from a polymer material.
 12. A rolling bearing comprising:an inner ring, an outer ring, at least one row of angular contactrollers disposed between raceways and guiding faces provided on therings, and a plurality of spacers disposed circumferentially between therollers and providing; an inner ring, an outer ring, at least one row ofangular contact rollers disposed between raceways and guiding facesprovided on the rings, and opposite inner and outer parts and oppositelateral flanges respectively adapted to come into contact with theraceways and the guiding faces of the rings, the inner and outer partsand/or the lateral flanges providing at least a contact surface with oneof the rings and at least a concave recess directed outwards towards thering.
 13. The rolling bearing according to claim 12, wherein therecesses of the spacers are filled with lubricant.
 14. A rolling bearingfor use in a wind turbine, the wind turbine comprising: a mast holding anacelle where blades are installed for rotating the nacelle with respectto the mast and/or for rotating/pitching each blade around itslongitudinal axis, the rolling bearing including; an inner ring, anouter ring, at least one row of angular contact rollers disposed betweenraceways and guiding faces provided on the rings, and a plurality ofspacers disposed circumferentially between the rollers and providing; aninner ring, an outer ring, at least one row of angular contact rollersdisposed between raceways and guiding faces provided on the rings, andopposite inner and outer parts and opposite lateral flanges respectivelyadapted to come into contact with the raceways and the guiding faces ofthe rings, the inner and outer parts and/or the lateral flangesproviding at least a contact surface with one of the rings and at leasta concave recess directed outwards towards the ring.